How to move tracking ownership when altering bureaux?

My Agency is hiring a new contractor to take over the google analytics and fb pixel accounts for our business. The current shop that has been managing it for us is saying that they cannot pass over the accounts since they have multiple properties under each account but can induce the new contractor an admin in facebook/ google for the property.

We are no longer dealing with this current shop moving forward so we would only like to have our bureau and contractor have access to our data and not the current shop we have been using.

Is this possible? Will the contractor after becoming admin be able to remove the previous stores access?